Hydraulic energy storage, often referred to as pumped hydro storage, is a method of storing energy by using water. During periods of low energy demand, excess electricity is used to pump water from a lower reservoir to a higher one. This process converts electrical energy into gravitational potential energy. When energy demand increases, the stored water is released back down to the lower reservoir, passing through turbines that generate electricity. This system is efficient and can quickly respond to changes in energy demand, making it a valuable component of the energy grid, especially in conjunction with renewable sources like solar energy and wind energy.